1. Field of the Invention
The present invention relates to manufacturing method for producing single-crystal silicon carbide that has low defects and high quality, and apparatus suitable for the same.
2. Related Art
Silicon carbide (SiC) has been developed as a semiconductor substrate for a power device because SiC has characteristics such as withstanding high voltage and high electron mobility. Generally, the single-crystal SiC is produced by a single crystal growth method called sublimation (the Modified Lely Method).
In the Modified Lely Method, silicon carbide source material is held in a graphite crucible, and a seed crystal is held in the graphite crucible to face the source material. The source material is heated to approximately 2200 to 2400° C., generating sublimed gas. The temperature of the seed crystal is kept lower than the source material by several tens up to several hundred degrees Celsius, causing the sublimed gas to recrystallize on a growth surface of the seed crystal and forming single SiC crystals.
However, there is a limit to growth with the Modified Lely Method as the source material decreases with the growth of single SiC crystals. Although new source material can be added, SiC is sublimed at a rate in which the ratio of Si to C is more than one, so that the concentration of the sublimed gas vacillates when the new source material is added in the growth process, thereby preventing high quality single SIC crystal growth.
An epitaxial growth method of single SiC crystals by Chemical Vapor Deposition (CVD) is disclosed in JP-A-11-508531 (U.S. Pat. No. 5,704,985). FIG. 4 shows a schematic cross sectional view of an apparatus for the epitaxial growth method described in the above-mentioned publication. As shown in FIG. 4, a susceptor 2 is used as a crucible and is disposed approximately at the center of a cylindrical case 1. The susceptor 2 is composed of high-purity graphite or the like. The SiC single crystal substrate is a seed crystal and is disposed on an upper, inner surface of the susceptor 2 to promote epitaxial growth. A heater 4 is provided at an outside portion of the case 1 to heat gases inside the susceptor 2.
The space surrounding the susceptor 2 is filled with a thermal insulator 5 composed of porous graphite. An inlet conduit 6, which is formed by the thermal insulator 5 and which has a funnel shape, is located under a bottom of the susceptor 2. A supplying portion 7 is located at a bottom of the case 1 to supply a mixture gas while outlet conduits 8 are disposed at a top of the susceptor 2 to exhaust the mixture gas. A conduit 9 is disposed at the upper side of the case 1 and communicates with the outside of the case 1.
In the apparatus described above, the mixture gas supplied by the supplying portion 7 is transferred to the susceptor 2 through the inlet conduit 6 formed by the thermal insulator 5. The gas mixture is heated by the heater 4 and epitaxial growth occurs on the seed crystal 3 to form a single silicon carbide crystal. Any remaining gas mixture is exhausted through the outlet conduits 8 disposed at the top of the susceptor 2 and the conduit 9, which is disposed at the upper side of the case 1.
However, in the CVD manufacturing method for producing a single silicon carbide crystal the inlet conduit 6 is composed of the graphite 5, and the heat from the susceptor 2 tends not to be transmitted to the inlet conduit 6. Therefore, the temperature of the gas mixture in the inlet conduit 6 is Low and the gas mixture is heated up rapidly when transferred to the susceptor 2. When the gas mixture is rapidly heated as described above, high quality single, silicon carbide crystals cannot be obtained.
Therefore, the temperature of the gas mixture should be increased in the inlet conduit 6 to a predetermined temperature and then supplied to the susceptor 2. However, when the temperature of the gas mixture is 500° C. or more, Si deposits may form on the wall surface of the inlet conduit 6. When the gas mixture is heated to a temperature where Si and C react with each other, SiC deposits may form on the wall surface of the inlet conduit 6. The deposits may obstruct the inlet conduit 6.
Furthermore, there is the possibility that, in a path 8, at an upper surface of the susceptor, which is narrow or in a path 9, which communicates with the outside of the upper chamber, Si which remains in the mixture gas or SiC as a product by reaction may deposit and block those paths.
The present invention addresses the above-mentioned problems, and an object thereof is to provide a manufacturing method of single silicon carbide crystals that is capable of preventing blockage caused by the mixture gas, and as another of its objects to provide an apparatus for the same.